I was getting sensor 2 codes but replaced both upstream sensors. Now Im getting 0130, 0135, 0155 and 0150 codes all relating to the downstream sensors. With these codes should I replace the 2 downstream sensors or is there something else going on? Thanx for any help.

 

I know I had codes for the pre cat o2's and replaced them. From what I have read on here the downstream ones are not that important for you just te environment because they are for emissions. I would not care if the downstream ones went bad I would leave them. I did notice a difference with my Idle replacing the upstreams.

 

replace both downstreams now too.

The ECU looks at the readings from the upstreams and the downstreams to
determine the condition of your CAT convertor.

The CARB and others want the CATs to scrub and burn bad stuff out of the exhaust stream.

So, now that the front O2's are working you will need to work the back O2's.

You can see some readings on the rear O2's on this page:

1997 Land Rover replace catalytic converter and head gaskets
Some of the pictures have readings on the Rear o2s

 

Thanx for the info. Just curious, are the upstream and downstream sensors the same?

 

Yes upstream and down stream sensors are the same.
The downstream ones only tell you if the cats are working or not, they have zero to do with engine fueling or run problems.
If the cats are out of range or the O2's are dead they will throw a code, depending on the code will determine your course of action.

If you still have your old front O2's then throw those in, clear the codes and see what happens.

 

The up and down stream sensors look different. The plugs are different too.

 

He is correct, I am wrong.
On the DI the fronts and rears are exactly the same, on the DII they are not.
I always forget that.

 

Yeah, seems to be running fine except for a idle issue I am having but no codes other than the 2 post sensors. Thanx

 

Did you happen to get the 02 from Atlantic British, quite a few people have had problem with there replacements. Where did you get them and were the OEM?

 

If you are4 at 100,000 miles or more, you should replace all 4 02 sensors and make sure you clean the connections for the front 02's cause they are prone to getting oil in them from leaking valve cover gaskets.